Today, my mortgage lender informed me I have a judgement from the State of NJ for$15,000 dating back to September of 1997. Unbeknowed to me. The only information they have for me is a docket number.

How do I look into this and get it removed?

Take the docket number and contact the courthouse in the county that the judgment was issued. Get as much information on it as you can. If you weren't properly served and the case was a default judgment, you should be able to get it dismissed based on improper service.